He studied with Karol Woytyla before his election as PopeJohn Paul II. Joos was already 80 years old when he was elevated to cardinal and therefore could not take part in any future conclave. His elevation as cardinal was seen by many as gratitude from Pope John Paul II towards his long time friend.

Before his nomination he was only known as a parish priest. Belgian media mistook him for another priest just after he was elevated to Cardinal.

After announcing his intention to elevate Father Joos to the Cardinalate, Pope John Paul also appointed him as a titular Bishop, and he was consecrated on October 7, 2003, days before the Consistory in which he was raised to the College of Cardinals. After his elevation, Cardinal Joos continued to live in the Diocese of Ghent, serving as a parish priest and as judicial vicar in ecclesiastical tribunals.

Interview of Gustaaf Joos with P-magazine

Joos gained notoriety in January 2004, when in an interview to Belgian P-Magazine, he said, about homosexuals:

"I am prepared to sign here in my blood that of all those who say they are lesbian or gay, at most five to 10 per cent are effectively lesbian or gay. All the rest are sexual perverts. I demand you write this down. If they come to protest on my doorstep, I don't care. I'm just speaking out on what thousands of people are thinking but never get a chance to say. Real homosexuals don't wander in the streets in colourful suits. Those are people who have a serious problem and have to live with that. And if they err, they will be forgiven."

"Politics, democracy. Don't make me laugh. The right to vote, what is that all about? I find it strange that a snot-nosed 18-year-old has the same vote as a father of seven. One has no responsibilities whatsoever, the other provides tomorrow's citizens. "